/*
struct TreeNode {
     int val;
     struct TreeNode *left;
     struct TreeNode *right;
 };
*/

#define swap(a,b) {struct TreeNode*t = a; a=b; b=t;}
struct TreeNode* mirrorTree(struct TreeNode* root){
    if (root == NULL) return NULL;
    swap(root->left, root->right);
    mirrorTree(root->left);
    mirrorTree(root->right);
    return root;
}

